49-cent brush may fix shuttle

WASHINGTON - A simple foam paint brush that costs only pennies at hardware stores could be an essential tool in returning the space shuttle to orbit, NASA's administrator said Wednesday.

Space agency engineers found that the brush may be just what astronauts need to spread a patching compound on a space shuttle's damaged heat shield while the craft is in orbit.

"This thing turns out to be one of the most valuable tools we could have invented," said Sean O'Keefe, head of the National Aeronautics and Space Administration. "We're going to buy it at Wal-Mart. We're not going to ask the Defense Department to requisition it out of stock."

A clerk at a Washington-area hardware store said a 1-inch foam brush sells for 49 cents and a 2-inch one costs 99 cents.

Designing and testing a way to repair damage in the shuttle's heat shield is an important part of NASA's efforts to return the space shuttle to orbit after the Feb. 1 accident that destroyed Columbia and killed seven astronauts.

The Columbia Accident Investigation Board determined that the shuttle broke apart when superheated air entered a hole in the heat shield on the leading edge of the left wing and melted internal aluminum supports. The accident has led the agency to ground the shuttle fleet.

Astronauts on Columbia and engineers at Mission Control were unaware of the extent of damage to the shuttle wing. Officials said there was no equipment on the shuttle to patch the wing even if the problem had been recognized.

Officials at the Johnson Space Center said the patching compound now under consideration could be used only for the part of the heat shield composed of lightweight tiles.

The nose of the shuttle and the leading edge of the wings are covered with panels of a different material, reinforced carbon-carbon. A carbon-carbon panel break led to the loss of Columbia.

Kelly Humphries, a spokesman at the space center, said repairing the carbon-carbon panels would require methods different from the tile repair. Among the techniques under consideration are a patch that could be internally bolted in place, an adhesive patch, or an overwrap that would envelop a heat shield breach.

For the lightweight tiles, engineers have found a sealant that is formed when two compounds are mixed. Tests showed that the combination expanded when heated. This led to a plan to "underfill" a hole and then let the heat of re-entry swell the patch and seal the hole.

Once they had a compound, the engineers then had to find a way for a spacewalking astronaut to apply the material while wearing a bulky space suit, gloves and a bubble helmet, O'Keefe said.

Experts looked at a variety of sophisticated tools made from exotic materials, he said. They settled on what he called "an elegant piece of sophisticated hardware" - a foam paint brush with a wooden handle.

O'Keefe said the foam brush avoided the problem of sticking to the sealant while the sealant was being spread in the hole. Other, more sophisticated tools became mired in the compound, he said.